Various industrial processes produce gaseous streams containing particulate and gaseous components (e.g., sulfur oxides and other sulfur compounds such as SO2, SO3, H2S and H2SO4). Such processes include, but are not limited to, for example, fossil fuel-fired power plants, natural gas treatment plants, refineries (e.g., fluid catalytic cracking (FCC) units), sulfur recovery units (SRUs), sulfuric acid plants, metal roasting operations, cement kilns and synthesis gas plants. Before such gas streams can be vented to the atmosphere, they must often be treated to remove the particulate and gaseous impurities.
Gas-liquid contacting devices in which the gaseous stream to be treated contacts an aqueous scrubbing liquid are employed to treat and remove particulate and gaseous impurities from gaseous industrial process streams. For example, in acid production processes, wet gas scrubbers may be used to remove acid gases and particulates from flue gas. There are many types of wet gas scrubbers in the marketplace. However, nearly all wet gas scrubbers share some common characteristics. In most cases, flue gas from the process is not saturated. However, before acid gases such as SO2 can be removed, the gas stream must be adiabatically saturated or “quenched”. Most scrubbers will have a section where liquid (e.g., the scrubbing liquid) is contacted with the incoming flue gas to adiabatically saturate, or “quench,” the gas stream. Only after the gas has been quenched can acid gas and SO2 removal occur. This is accomplished in two steps: 1) the acid gases are absorbed into the scrubbing liquid; and 2) once absorbed, the acid gases react with a reagent, forming reaction by-products that are then removed from the clean gas. In general, all scrubbers have a method for removing the water droplets and reaction by-products from the gas before the treated gas is discharged from the scrubber.
Gas-liquid contacting devices capable of handling hot and/or corrosive gaseous effluents and operating at high overall liquid to gas ratio (L/G) are often preferred. For example, gas scrubbing systems comprising a reverse jet scrubber of the type disclosed in U.S. Pat. No. 3,803,805 and sold under the trademark DYNAWAVE by MECS, Inc. (Chesterfield, Mo. U.S.A. 63017) are particularly suited for effective separation and removal of particulate and gaseous components from hot gas streams.
Reverse jet scrubbers typically include a gas inlet system and a gas-liquid disengagement vessel downstream of the gas inlet system. The gas inlet system includes a scrubbing vessel that receives the hot, corrosive gas and brings the gas in contact with an intense spray of scrubbing liquid emitted from one or more reverse jets to quench the gas stream and absorb acid gas impurities into the scrubbing liquid and remove particulate contaminants. To prevent thermal and corrosive damage in the vicinity of the hot gas inlet, the upper region of the reverse jet scrubbing vessel is kept cool and cleaned by a continuously flowing liquid film produced by feeding a portion of the scrubbing liquid into the reverse jet scrubber my means of an overflow or leaping weir as described, for example in Canadian Published Application No. 2,050,710. In particular, the overflow weir forms a continuous, flowing film of liquid (such as circulating scrubbing liquid) along the interior surface of the scrubbing vessel in the vicinity of the hot gas inlet. The overflow weir typically includes a weir trough or bowl that fills with liquid and overflows into the scrubbing vessel. This film of flowing liquid protects the equipment from high temperature, and/or excessive corrosion.
However, the effectiveness of reverse jet scrubbing systems can sometimes be adversely affected by the build-up of suspended particles in the circulating scrubbing liquid. The circulating liquid introduced into the scrubbing vessel through the weir often contains suspended particles, such as metal oxides and/or fly ash, that can settle out and deposit in the weir. During operation of the gas inlet system, some of the particulates disengage from the liquid in the weir trough and settle at the bottom of the weir trough. Over time, the particulates may accumulate in the weir trough, leading to problems such as non-uniform overflow of liquid in the weir. In turn, the non-uniform overflow of liquid may lead to dry areas on the interior surface of the scrubbing vessel, which can result in corrosion and ultimately failure of the gas inlet system.
Particulate impurities can be purged from the scrubbing liquid circulating in a reverse jet wet scrubber system. For example, external drains in fluid communication with the weir trough and actuated on an intermittent basis can be used to eliminate the solids that settle out in the weir bowl. In one example, the external drain includes a funnel at the bottom of the weir trough in which disengaged particulates settle and accumulate. An external valve is fluidly connected to the funnel. The valve is periodically opened to allow for flushing and removal of particulates in the funnel.
Although the overflow weir and the external drains have worked quite well in most applications, the inventors of the claimed invention have identified several potential issues with the overflow weir and the external drains, as described below. The inventors do not concede that these issues are known in the prior art or readily identifiable to those of ordinary skill in the art.
The external drains may be costly to fabricate and install at the site, and require external piping, valves, wiring and heat tracing. Moreover, because these external drains operate on an intermittent basis, if the purge cycle is disrupted for any reason, including valve failure, operator error, equipment failure, etc., the liquid film can be disrupted and the equipment damaged by the corrosive gas. If overflow was disrupted along the upper end of the weir, for whatever reason, a dry spot(s) may occur in the scrubbing vessel. The dry spot may lead to corrosion and/or overheating of that area of the vessel, and ultimately failure of the gas inlet system. Moreover, if solids build up too quickly, the external drains could become clogged. When this happens, additional solids would settle until flow over the upper end of the weir is disrupted. As another example, the external drain valves could either fail to open, which would cause solids build-up, or they could remain open too long, and disrupt flow over the weir.
Accordingly, in view of the above-identified potential issues with conventional gas inlet systems, a need persists for improved weir and gas inlet system designs for wet gas scrubbers that provide for effective, continuous removal of accumulating solid impurities from the circulating scrubbing liquid.